The high speed downlink packet access technology introduces a new transmission channel namely a High Speed Downlink Shared Channel (HS-DSCH), which is used for bearing the actual user data accessed by the high speed downlink packet. The high speed packet access technology introduces new physical channels. A High Speed Shared Control Channel (HS-SCCH) is one of the newly added physical channels and is used for bearing certain important control signaling information. The working process of HS-DSCH is always accompanied by the HS-SCCH.
In the high speed downlink packet access technology, in all cells in a soft handover active set, there is only one serving HS-DSCH cell. Characteristics of the serving HS-DSCH cell lie in that the HS-DSCH and HS-SCCH will be only transmitted in this cell, and corresponding uplink feedback will be received. In the multi-carrier high speed packet access technology, each layer of carriers will has its own independent soft handover active set. The serving HS-DSCH cell in a primary carrier soft handover active set is called as a primary carrier serving HS-DSCH cell or a primary serving HS-DSCH cell. The serving HS-DSCH cell in an auxiliary carrier soft handover active set is called as an auxiliary carrier serving HS-DSCH cell or an auxiliary serving HS-DSCH cell.
In the high speed downlink packet access technology, the adaptive coding and modulation technology is adopted to replace the traditional dedicated channel power control technology. A fundamental principle of the adaptive coding and modulation technology is to match a modulation and coding scheme of the system with an average channel condition in the process of each terminal transmitting data. Signal power of the data transmission keeps unchanged within a subframe period, but modulation and coding formats are changed in order to match the current signal quality or channel condition. The change of data transmission rate is implemented by changing the modulation and coding formats of the physical channels. A terminal reports a channel quality indication to a node B according to a situation of the current downlink channel (i.e. a High Speed Physical Downlink Shared Channel (HS-PDSCH)), and the node B can match a coding rate and modulation mode of a downlink channel with the optimal performance according to this channel quality indication.
A reporting rule of the channel quality indication is: within an unlimited observation time, the terminal reporting a maximum channel quality indication value to the node B. In order to obtain a correct channel quality indication value, the terminal needs to estimate total received power of the high speed physical downlink shared channel, and according to the total received power of the high speed physical downlink shared channel and a curve of channel quality indication values, the terminal obtains a corresponding channel quality indication value.
The total received power of the high speed physical downlink shared channel is estimated using the following formula: total received power of high speed physical downlink shared channel=total received power of common pilot channel combination+measured power deviation+reference power adjustment amount. Wherein: the total received power of common pilot channel combination is measured by the terminal; the reference power adjustment amount depends on a grade classification of the terminal and the channel situation reported at that time, and its value is generally 0; the measured power deviation is defined as a measured power deviation of transmitted power of high speed physical downlink shared channel relative to the total received power of common pilot channel combination, and thus a Controlling Radio Network Controller (CRNC), to which a cell belongs, possesses radio resources of this cell. The measured power deviation in the formula is configured by the CRNC, to which the cell belongs, for the terminal.
As shown in FIG. 1, the controlling radio network controller of a cell 1 is a radio network controller 1, and when a terminal 1 uses the high speed downlink packet access technology in the cell 1, the cell 1 is a serving HS-DSCH cell of the terminal 1. The radio network controller 1 will configure a measured power deviation of the cell 1 to the terminal 1. The terminal 1 measures total received power of the common pilot channel combination of the cell 1, and determines the reference power adjustment amount according to the grade classification of the terminal 1 and the channel situation reported at that time. Then, the terminal uses the above formula to estimate the total received power of the high speed physical downlink shared channel of the cell 1.
An Interconnection of Radio Network Controller (IUR) interface is an interface used for performing singling and data interaction with other radio network controllers by a radio network controller, and it is an interconnected tie among radio network subsystems.
When a terminal establishes a connection to a wireless access network and a soft handover occurs at the IUR interface, resources of more than one radio network controller will be used, and different radio network controllers play different roles at this point as follows:
A Serving Radio Network Controller (SRNC): a radio network controller keeping the terminal connected with interfaces of a core network is the serving radio network controller, and the serving radio network controller is responsible for data transmission between the core network and the terminal and for forwarding and receiving interface signalings between the serving radio network controller and the core network, it is responsible for performing the radio resource control, and it is responsible for performing layer 2 processing on data of air interfaces, and executing basic operations of radio resource management, such as handover decision, outer loop power control, and conversion from parameters borne by wireless access to air interface transmission channel parameters and so on;
A Drift Radio Network Controller (DRNC): the drift radio network controller is another radio network controller except the serving radio network controller, and the drift radio network controller controls cells used by the terminal, and if necessary, the drift radio network controller can perform macro diversity combining Unless the terminal uses a common transmission channel, the drift radio network controller will not perform layer 2 processing on user plane data of the terminal, but it just transparently transfers air interface data to the serving radio network controller through routing of the IUR interface. The number of drift radio network controllers of one terminal can be more than one.
In engineering applications, when encountering a scenario shown in FIG. 2, the controlling radio network controller of the cell 1 is the radio network controller 1, the controlling radio network controller of a cell 2 is a radio network controller 2. The IUR interface exists between the radio network controller 1 and the radio network controller 2. The terminal 1 moves from the cell 1 to the cell 2, the radio network controller 1 is the serving radio network controller of the terminal 1, and the radio network controller 2 is the drift radio network controller of the terminal 1. The terminal 1 moves from the cell 1 to the cell 2, the cell 1 is a current serving HS-DSCH cell of the terminal 1, and the cell 2 is a target serving HS-DSCH cell to which the terminal 1 will hand over from the current serving HS-DSCH cell, that is, the terminal 1 wants to perform a serving HS-DSCH cell handover, i.e. the terminal 1 wants to hand over from the serving HS-DSCH cell, namely the cell 1, to the cell 2. The problem of call drop in the terminal will occur.